1. Field of the Invention
The present invention relates to a fuel injection device of an internal combustion engine.
2. Description of Related Art
FIG. 9 shows one previously proposed fuel injection device (i.e., injector) 200 of an internal combustion engine (hereinafter, simply referred to as an engine). In the fuel injection device 200, a cylindrical tubular member 202 receives a valve member 210, a movable core 212 and a stationary core 214. The tubular member 202 has a first magnetic segment 203, a magnetically resistive segment 204 and a second magnetic segment 205, which are arranged in this order from a downstream end (lower end in FIG. 9) of the tubular member 202, which is located on an injection hole 208 side. The movable core 212 reciprocates together with the valve member 210, which enables and disables injection of fuel from injection holes 208. The stationary core 214 is arranged on an upstream side of the movable core 212 in opposed relationship to the movable core 212. The stationary core 214 is secured to the tubular member 202 by welding at a weld 220.
Positioning of the stationary core 214 relative to the tubular member 202 and welding of the stationary core 214 to the tubular member 202 are time consuming and tedious operations.
Furthermore, the position of the stationary core 214 could be deviated in a reciprocating direction of the valve member 210 during the welding of the stationary core 214 to the tubular member 202. When the position of the stationary core 214 is deviated in the reciprocating direction of the valve member 210, the maximum size of a gap formed between the stationary core 214 and the movable core 212 changes. This causes device-to-device variations (i.e., injector-to-injector variations) in a fuel injection rate with respect to a predetermined control electric current waveform, so that adjustment of the fuel injection amount needs to be performed on each fuel injection device. This causes an increase in the number of assembling steps of the fuel injection device.
Another previously proposed fuel injection device is disclosed in Unexamined Japanese Patent Publication No. 11-132127. In the previously proposed fuel injection device, a stationary core (stator), a movable core (armature) and a valve member are received in a tubular member (main tubular body). When electric current is supplied to a coil arranged around the tubular member, the stationary core, the tubular member and the armature form a magnetic circuit, so that the armature is attracted to the stationary core to lift the valve member from a valve seat. In the fuel injection device, the stationary core is secured to an inner peripheral wall surface of the tubular member, for example, by press fitting the stationary core into the tubular member.
Recent years, regulations regarding emissions of the engines are being tightened. Thus, relatively precise adjustment of the fuel injection amount of the fuel injection device is required to reduce cylinder-to-cylinder variations in air-fuel ratio. The relatively precise adjustment of the fuel injection amount can be achieved in the following way. That is, the stationary core is press fitted into the tubular member while the fuel injection amount is measured, and the stationary core is secured to the tubular member at a point where a desired fuel injection amount is measured.
However, in the press fitting of the stationary core into the tubular member, an outer peripheral edge of a downstream end of the stationary core could scrape the inner peripheral wall of the tubular member, so that scraped debris falls in a fuel pressure chamber. Also, a welded connection of the tubular member can be damaged by press fitting load applied from the press fitted stationary core. Furthermore, a magnetic property of the magnetic circuit can be deteriorated by deformation of the stationary core. The placement of the scraped debris in the fuel pressure chamber and the deterioration of the magnetic property of the magnetic circuit deteriorate not only the adjustment accuracy of the fuel injection amount but also response of the fuel injection device. Furthermore, the damage to the welded connection of the tubular member causes a reduction in yield.